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Publication: Structured functional domains of myelin basic protein

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Title Structured functional domains of myelin basic protein
Authors/Editors* V.V. Bamm, M. De Avila, G.S.T. Smith, M.A.M. Ahmed, G. Harauz
Where published* Biophysical Journal
How published* Journal
Year* 2011
Volume 101
Number 5
Pages 1248-1256
Publisher Cell Press
Keywords
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Abstract
The 18.5-kDa myelin basic protein (MBP), the most abundant isoform in human adult myelin, is a multifunctional, intrinsically disordered protein that maintains compact assembly of the sheath. Solution NMR spectroscopy and a hydrophobic moment analysis of MBP’s amino-acid sequence have previously revealed three regions with high propensity to form strongly amphipathic a-helices. These regions, located in the central, N- and C-terminal parts of the protein, have been shown to play a role in the interactions of MBP with cytoskeletal proteins, Src homology 3-domain-containing proteins, Ca2þ-activated calmodulin (Ca2þ-CaM), and myelin-mimetic membrane bilayers. Here, we have further characterized the structure-function relationship of these three domains. We constructed three recombinant peptides derived from the 18.5-kDa murine MBP: (A22–K56), (S72–S107), and (S133–S159) (which are denoted a1, a2, and a3, respectively). We used a variety of biophysical methods (circular dichroism spectroscopy, isothermal titration calorimetry, transmission electron microscopy, fluorimetry, and solution NMR spectroscopy and chemical shift index analysis) to characterize the interactions of these peptides with actin and Ca2þ-CaM. Our results show that all three peptides can adopt a-helical structure inherently even in aqueous solution. Both a1- and a3-peptides showed strong binding with Ca2þ-CaM, and both adopted an a-helical conformation upon interaction, but the binding of the a3-peptide appeared to be more dynamic. Only the a1-peptide exhibited actin polymerization and bundling activity, and the addition of Ca2þ-CaM resulted in depolymerization of actin that had been polymerized by a1. The results of this study proved that there is an N-terminal binding domain in MBP for Ca2þ-CaM (in addition to the primary site located in the C-terminus), and that it is sufficient for CaM-induced actin depolymerization. These three domains of MBP represent molecular recognition fragments with multiple roles in both membrane- and protein-association.
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